The present invention relates to semiconductor packages and fabrication methods thereof, and more particularly, to a FCBGA (flip-chip ball grid array) semiconductor package with a heat-dissipating device and a method for fabricating the semiconductor package.
FCBGA (flip-chip ball grid array) semiconductor packages are an advanced packaging technology, which is characterized by implanting a plurality of solder bumps on an active surface, a surface formed with electronic components, of a chip that is electrically connected to a substrate by bonding the solder bumps to the substrate. Compared to BGA semiconductor packages, flip-chip package structure is free of forming bonding wires for chip-to-substrate electrical connection; without having to fabricate bond fingers on a substrate for wire-bonding, thereby effectively reduce the package size.
With high-integration development of semiconductor packages and chips, it becomes a critical problem to efficiently dissipate heat produced by operation of the semiconductor packages and chips.
Therefore, as shown in FIG. 5, U.S. Pat. No. 5,798,567 disclose a FCBGA semiconductor package 1 mounted on a circuit board 10 such as a printed circuit board (PCB). This semiconductor package 1 is provided with a chip 12 mounted on a substrate 11 in a flip-chip manner, wherein the chip 12 is implanted with a plurality of first solder bumps 13, and electrically connected to the substrate 11 by bonding the first solder bumps 13 to the substrate 11. A plurality of second solder bumps 14 are implanted on the substrate 11, for allowing the semiconductor package 1 to be bonded to the circuit board 10 by means of the second solder bumps 14, wherein a conductive adhesive 15 is applied between the chip 12 and the circuit board 10, such that heat produced by operation of the chip 12 can be transmitted through the conductive adhesive 15 to the circuit board 10 for dissipation.
However, the above conventional semiconductor package 1 requires additional processes of surface mount technology (SMT) for applying the conductive adhesive 15 over the circuit board 10, thereby increasing process complexity and costs in package fabrication. Moreover, in practice, the conductive adhesive 15 is a perfect heat transmission material, and therefore not capable of optimally dissipating the heat produced from the chip 12.
Another FCBGA semiconductor package 1xe2x80x2 is similar in structure to the above semiconductor package 1, and thereby also illustrated by FIG. 5. This semiconductor package 1xe2x80x2 differs from the above semiconductor package 1 in that, a metallic heat sink 15xe2x80x2 is used, instead of the conductive adhesive 15, for connecting the chip 12 to the circuit board 10, so as to allow the heat produced from the chip 12 to be transmitted through the heat sink 15xe2x80x2 to the circuit board 10 for dissipation.
However, with the heat sink 15xe2x80x2 being interposed between the chip 12 and the circuit board 10, during a solder-reflow process for bonding the heat sink 15xe2x80x2 to the circuit board 10, the heat sink 15xe2x80x2 of relatively large area would be unevenly heated, which possibly results in forming of voids or even popcorn effect, thereby adversely affect the quality of fabricated products. Moreover, due to mismatch in coefficient of thermal expansion (CTE) between the metallic heat sink 15xe2x80x2 and the chip 12, delamination may undesirably occur at interface between the heat sink 15xe2x80x2 and the chip 12, which would undesirably increase resistance of heat dissipation and degrade heat-dissipating efficiency, as well as reduced yield.
Therefore, the above drawbacks of a semiconductor package for assuring quality thereof and effectively dissipating heat produced thereby is a critical issue to solve.
An objective of the present invention is to provide a FCBGA (flip-chip ball grid array) semiconductor package with a heat-dissipating device and a method for fabricating the same, so as to effectively improve heat-dissipating efficiency of the semiconductor package.
Another objective of the present invention is to provide a FCBGA semiconductor package with a heat-dissipating device and a method for fabricating the same, without increasing process complexity of mounting the semiconductor package on a circuit board.
A further objective of the present invention is to provide a FCBGA semiconductor package with a heat-dissipating device and a method for fabricating the same, so as to prevent forming of voids or popcorn effect for the semiconductor package, thereby assuring quality of fabricated products.
A further objective of the present invention is to provide a FCBGA semiconductor package with a heat-dissipating device and a method for fabricating the same, so as to prevent delamination for the semiconductor package, thereby improving yield of fabricated products.
In accordance with the above and other objectives, the present invention proposes a FCBGA semiconductor package with a heat-dissipating device, and a method for fabricating the semiconductor package. The FCBGA semiconductor package comprises: a substrate having an upper surface and a lower surface opposed to the upper surface; at least one first chip mounted on and electrically connected to the upper surface of the substrate; at least one second chip mounted on the lower surface of the substrate in a flip chip manner, the second chip having an active surface and a non-active surface opposed to the active surface, allowing the second chip to be electrically connected to the substrate by bonding a plurality of first solder bumps to the active surface of the second chip and the lower surface of the substrate; a plurality of second solder bumps implanted on the lower surface of the substrate at an area exclusive of the second chip; a heat-dissipating device composed of a heat sink and a plurality of thermally conductive bumps, wherein the heat sink has an upper surface and a lower surface opposed to the upper surface, allowing the upper surface to be attached to the non-active surface of the second chip, and the thermally conductive bumps are implanted on the lower surface of the heat sink, and a circuit board for accommodating the thermally conductive bumps and the second solder bumps thereon in a manner that, the thermally conductive bumps are interposed between the heat sink and the circuit board, and the second solder bumps are interposed between the substrate and the circuit board.
The method for fabricating the above FCBGA semiconductor package comprises the steps of: preparing a substrate having an upper surface and a lower surface opposed to the upper surface; mounting at least one first chip on the upper surface of the substrate, allowing the first chip to be electrically connected to the substrate; mounting at least one second chip on the lower surface of the substrate in a flip chip manner, the second chip having an active surface and a non-active surface opposed to the active surface, allowing the second chip to be electrically connected to the substrate by bonding a plurality of first solder bumps to the active surface of the second chip and the lower surface of the substrate; implanting a plurality of second solder bumps on the lower surface of the substrate at an area exclusive of the second chip; preparing a heat-dissipating device composed of a heat sink and a plurality of thermally conductive bumps, wherein the heat sink has an upper surface and a lower surface opposed to the upper surface, allowing the upper surface to be attached to the non-active surface of the second chip, and the thermally conductive bumps are implanted on the lower surface of the heat sink; and providing a circuit board for accommodating the thermally conductive bumps and the second solder bumps thereon in a manner that, the thermally conductive bumps are interposed between the heat sink and the circuit board, and the second solder bumps are interposed between the substrate and the circuit board.
Combined thickness of the second chip, first solder bump, heat sink and thermally conductive bump is equal to and slightly smaller than height of the second solder bump. Therefore, bottoms of the thermally conductive bump and the second bond pads are coplanar to be bonded to the circuit board. The semiconductor package can operate with electrical connection to the circuit board via the second solder bumps. And, heat produced by operation of the semiconductor package can be transmitted through the heat-dissipating device (heat sink and thermally conductive bumps) to the circuit board, and dissipated to outside of the circuit board via the thermal pads and the thermal vias, thereby effectively improving heat-dissipating efficiency of the semiconductor package.
In another embodiment, the heat sink is formed with at least one protruding portion peripherally protruding from the upper surface of the heat sink toward the substrate to reach the lower surface of the substrate. With the protruding portion abutting against the substrate, heat produced from operation of the semiconductor package can be more efficiently transmitted through the heat sink and thermally conductive bumps to the circuit board for dissipation, thereby further improving heat-dissipating efficiency of the semiconductor package.
Besides improvement in heat-dissipating efficiency, the above semiconductor package can also provide other significant benefits by using a heat-dissipating device composed of a heat sink and a plurality of thermally conductive bumps, for eliminating drawbacks in the prior art through the use of a conductive adhesive with a heat sink. First, compared to the conventional conductive adhesive, combination of the heat sink and the thermally conductive bumps provides better heat-dissipating efficiency for the semiconductor package. And, the thermally conductive bumps and the second solder bumps are simultaneously mounted on the circuit board, without undesirably increasing process complexity of surface mount technology (SMT). Moreover, as contact area between the thermally conductive bumps and the circuit board is relatively small, forming of voids or popcorn effect caused by uneven heating to a conventional heat sink can be prevented during a solder-reflow process. In addition, the heat sink is made of a material similar in coefficient of thermal expansion (CTE) to the second chip, thereby eliminating problems of delamination between a conventional heat sink and a chip due to CTE mismatch. Therefore, quality and production yield of the semiconductor package can be well assured through the use of the heat-dissipating device.